1. Field of the Invention
The present invention relates to a dielectric polymer material which possesses a dielectric constant varying at a high level to a less extend in a wide range of temperatures.
2. Brief Description of the Prior Art
Japanese Patent early Publication No. 69,000/1977 (Patent Publication No. 42,443/1980) discloses dielectric polymer materials which are composed of bipolymers consisting of ethylene trifluoride and vinylidene fluoride and possess a high dielectric constant. The bipolymers, however, have a high dependence of their dielectric constants upon temperature and their dielectric constants may be varied to a great extent with a slight change in usually practically utilizable temperatures ranging from room temperature to 100.degree. C. For example, where the amount of vinylidene fluoride is 55 mol%, the dielectric constant which is about 20 at about 50.degree. C. jumps to a high dielectric constant of about 57 when the temperature is raised to about 85.degree. C. Although temperatures exhibiting maximum dielectric constants vary with compositions of the bipolymers, they have a common characteristic property that the dependence of their dielectric constants upon temperature is great regardless of the compositions of the bipolymers. The high dependence of a dielectric constant upon temperature means that, for example, where a rapid change in temperature is occurred in a capacitor, a rapid change in the function of storing electricity is also caused and that, where a dielectric material is employed as a binder of dispersion electroluminescence or the like, a rapid change in temperature gives rise to a rapid reduction in brightness.
U.S. Pat. No. 3,053,818 to Honn et al. discloses trifluorochloroethylene interpolymers obtainable by interpolymerizing trifluorochloroethylene, vinylidene fluoride and another fluoroolefin including trifluoroethylene. The interpolymers are produced from monomeric mixtures comprising said three components, in which the trifluorochloroethylene and the vinylidene fluoride monomers are each present in an amount of at least 15 mole percent and the other fluoroolefin monomer is present in an amount of at least 5 mole percent. The trifluorochloroethylene interpolymers cannot provide an almost constant dielectric constant over a wide temperature range and a high dielectric constant.
Polyvinylidene fluoride possesses a dielectric constant of about 8 to 16 at room temperature although the dielectric constant may be varied with conditions of orientation of the dielectric material and does not relatively undergo change in temperature. Accordingly, there has been demanded a dielectric material which possesses a higher dielectric constant and does not undergo change in a dielectric constant to a great extent in a wide range of temperatures.